During development of a fetus in utero, blood is generally oxygenated by the mother's placenta, not the fetus' developing lungs. Most of the fetus' circulation is shunted away from the lungs through specialized vessels or foramens that are open during fetal life, but generally close shortly after birth. Occasionally, however, these foramen fail to close and create hemodynamic problems, which may ultimately prove fatal unless treated.
One defect that may occur is a patent foramen ovale (“PFO”), which may occur between the left and right atria of the heart. During fetal life, an opening called the foramen ovale allows blood to pass directly from the right atrium to the left atrium (bypassing the lungs). Thus, oxygenated blood from the placenta may travel through the vena cava into the right atrium, through the foramen ovale into the left atrium, and from there into the left ventricle for delivery via the aorta to the fetus' body. After birth, with pulmonary circulation established, the increased left atrial blood flow and pressure causes the functional closure of the foramen ovale. This closure is then followed by the anatomical closure of the foramen ovale.
In some humans, however, the foramen ovale fails to completely close. This condition can pose serious health risks for the individual, particularly if the individual has other heart abnormalities. For example, recent studies suggest an association between the presence of a patent foramen ovale and the risk of paradoxical embolism or stroke. See P. Lechat J et al., Prevalence of Patent Foramen ovale in Patients with Stroke, N. Engl. J. Med. 1988;318: 1148-1152.
Still other septal defects may occur within a septum between the various chambers of the heart, such as atrial-septal defects (ASDs), ventricular-septal defects (VSDs), and the like. To close such defects, open heart surgery may be performed to ligate and close the defect. Such procedures are obviously highly invasive and pose substantial morbidity and mortality risks.
Alternatively, catheter-based procedures have been suggested. These may involve introducing umbrella or disk-like structures into the heart that include opposing expandable structures connected by a hub or waist. Generally, the device is inserted through the defect, and the expandable structures are deployed on either side of the septum to secure the tissue surrounding the defect between the umbrella or disk-like structure in an attempt to seal and close the defect. Such devices, however, involve frame structures that often support membranes, either of which may fail during the life of the patient being treated, opening the defect and/or releasing segments of the structure within the patient's heart.
Accordingly, apparatus and methods for closing septal defects, and in particular a patent foramen ovale, would be considered useful.